1. Field of the Invention
The present invention relates to a push-pull switching power converter and, in particular, to a power converter, such as an AC-to-DC converter and a DC-to-DC converter, using a pair of switching devices.
2. Description of the Related Art
Switching power supply circuits having a pair of switching devices and carrying out desired power conversion by switching on and off the switching devices control on and off of each switching device using a rectangular wave pulse (refer to, for example, Japanese Patent Application Laid-Open No. 4-364362).
Such switching power supply circuits also carry out dead-time control to prevent a through current flowing between the pair of switching devices and carry out timing control (zero cross control) to determine a timing for converting a logical level of the rectangular wave pulse by detecting the zero cross of voltage or current at a predetermined point.
In known switching power supply circuits, as described above, a dead-time control circuit and a zero-cross control circuit are essential, thus complicating the structure. Furthermore, since the signal wave used for switching is a rectangular pulse wave, switching noise tends to occur. Therefore, the power conversion efficiency is decreased, which is a problem.